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Kate Becker: Dream of new planets in the solar system lives on

By Kate Becker

For the Camera

Posted:
06/09/2016 03:23:47 PM MDT

Updated:
06/10/2016 06:06:58 AM MDT

Kate Becker The Visible Universe

I used to have this recurring dream: Walking through the house I grew up in, I would notice a door I'd never seen before, leading to a hidden room I'd never been in. It's a common dream, apparently — just Google it. But the notion that a familiar home might contain some still-unexplored space isn't limited to dreamland. It's happening right here in the solar system, too.

For 99.9 percent of human history, the only rooms in the cosmic house were the eight solar system bodies you can see with your naked eye — the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn and, of course, Earth. Then telescopes came along, and new doors started opening. Suddenly, there were moons around Jupiter and Saturn, and Uranus and its little lunar brood beyond them, too. Uranus, in turn, pointed the way to even more new territory: because Uranus' real-life position on the sky didn't align with the orbit predicted by astronomers' equations, astronomers inferred the presence of another unseen world. Neptune was discovered in 1846, the first planet to be mathematically predicted before it was observed.

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The celestial house wasn't complete, though. Neptune couldn't explain all the deviations in Uranus' orbit, astronomers thought, and Neptune itself swung away from the arc predicted by Newton's laws. Astronomers reckoned that there must be another, undiscovered "Planet X," even further out. The search went on for more than eight decades, until Clyde Tombaugh discovered Pluto, and the mystery was considered solved — until, later on, astronomers realized that Pluto was much too small to be the cause of Neptune and Uranus' orbital aberrations. (They were ultimately chalked up to error.)

The story doesn't end there, of course. In the 1990s, astronomers began finding objects — calling them "worlds" or "planets" would be somewhat too generous — orbiting beyond Neptune in a zone called the Kuiper Belt. Meanwhile, the search for a true "Planet X" continued, teetering between rigorous research and pseudoscience. There were legitimate contenders to the title: In 1999, for instance, astronomers proposed that a hypothetical gas giant could be floating among the comets in the solar system's farthest outlying territory, but when they searched for it in millions of spacecraft images, they came up empty-handed.

Now, astronomers again have clues that may point the way to a new world, though it's now nicknamed "Planet Nine" — the ironic byproduct of the solar system's growing census being, of course, that the number of known planets actually went down, from nine to eight, when Pluto was reclassified. The evidence for the new Planet Nine: a strange clustering of objects in the Kuiper Belt that seems to be best explained by the gravitational influence of a still-unseen gas giant orbiting far beyond the solar system's other planets — a sort of planetary annex to the solar system's central rooms.

But is Planet Nine really there? Leading with math has paid off before in the search for new solar system objects — remember Neptune? — but in this case, the math also presents a puzzle. That's because astronomers are struggling to explain how a planet could wind up so far away from the Sun. Did Planet Nine form way out there in the solar boondocks? Was it towed out by the gravity of a passing star? Did a weird game of planetary pinball fire it into the hinterland? Or did the Sun steal it away from some other solar system? Multiple teams of astronomers are using computer simulations to investigate these scenarios, but the real test will come when we get our first glimpse of the planet.

If, that is, Planet Nine really exists. For now, it's too soon to say whether we're about to unlock the door to our solar system's secret room — or if we'll soon wake from the same old dream.

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